Problem: Expand.
Explanation: $\begin{aligned} &\phantom{=}({2z-1})(z^2-2z+1) \\\\ &={2z}(z^2-2z+1){-1}(z^2-2z+1) \end{aligned}$ $\begin{aligned} &=2z^3-4z^2+2z-z^2+2z-1 \\\\ &=2z^3-5z^2+4z-1 \end{aligned}$